CN103956919A - Simplified model forecasting control method of network voltage unbalance three-level rectifier - Google Patents
Simplified model forecasting control method of network voltage unbalance three-level rectifier Download PDFInfo
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Abstract
The invention belongs to the field of converter control, and relates to a simplified model forecasting control method of a network voltage unbalance three-level rectifier. The simplified model forecasting control method of the network voltage unbalance three-level rectifier comprises the steps that (1) positive and negative sequence separation is carried out on three-phase network voltage and current to obtain positive and negative sequence components; (2) coordinate transformation is carried out on three-phase positive sequence voltage and current to obtain positive sequence voltage and current under a two-phase static coordinate system; (3) according to the three-phase positive sequence voltage, three levels are changed into two levels in an order reduction mode through reference voltage; (4) an active power reference value and a current reference value are calculated; (5) a current forecasting value of the rectifier, a direct current side capacitance voltage forecasting value and the changing number of switching elements are calculated; (6) current control, neutral-point potential control and switching frequency control are forecast according to a model, and the best switching state is selected. The simplified model forecasting control method of the network voltage unbalance three-level rectifier can effectively suppress double-frequency fluctuation of input power of the rectifier, lower the switching frequency of the elements, shorten circulation calculation time, control neutral-point potential balance, and improve the operation efficiency of the system.
Description
Technical field
The present invention relates to a kind of control method of unbalanced source voltage three level rectifiers, specifically, relate to a kind of unbalanced source voltage three level rectifier low switching frequency simplified model forecast Control Algorithm.
Background technology
Along with the fast development of novel power transistor and technology, Three-Phase PWM Rectifier has the feature of voltage on line side sineization, unity power factor operation and energy in bidirectional flow, therefore in mesohigh large-power occasions, has good application prospect.Obtaining under the condition of identical control function, the switching frequency of three-level PWM rectifier reduces by one times, and current harmonics can effectively reduce, so the research of high-power three-level PWM rectifier and control thereof also becomes focus, simultaneously Model Predictive Control Algorithm is because of the advantage that its algorithm is simple, current tracking precision is good, control switch frequency is low, dynamic response is good, and is widely used in the design of rectifier control system.
And the advantage of above-mentioned rectifier realizes when line voltage balance, but in Practical Project, there will be three phase network Voltage unbalance situation, cause DC side electric current can produce 6,12,18 etc. 6 integral multiple characteristic harmonics and 2,4,6, the uncharacteristic harmonics of 8 grades, in alternating current, will there are the subharmonic such as 3,5,7,9, make rectifier occur irregular operating state, when serious, can make system deterioration.The feature of rectifier control system during for unbalanced source voltage, the control strategy adopting should guarantee that current on line side is sinusoidal, and can suppress direct voltage two frequency multiplication pulsation.Existing solution adoption rate integration (PI), ratio resonance (PR) controller and some gamma controllers are controlled current inner loop, but still there are the accurately precision of follow current and the problem of response speed, especially in high-power applications occasion, switching frequency reduces the generation to PWM inertial element and has a strong impact on, and makes it cannot realize the stable operation of system.
Due to above-mentioned shortcoming, the low switching frequency simplified model forecast Control Algorithm that is necessary to design three level rectifiers under a kind of unbalanced electric grid voltage, when control system is moved, can control effectively to three-phase imbalance, and improve the response speed of system, improve the control performance of system.
Summary of the invention
The simplified model forecast Control Algorithm that the object of this invention is to provide three-level PWM rectifier under a kind of unbalanced source voltage, the method can effectively suppress two frequencys multiplication of three level rectifier input active power under unbalanced source voltage, has improved system and has controlled effect; Under unbalanced electric grid voltage, the switching frequency of three level rectifiers is controlled, reduce device switching loss; Three level model predictive control algorithms are simplified simultaneously, reduced computing time, improved control efficiency.
For achieving the above object, three level rectifier simplified model forecast Control Algorithm under a kind of unbalanced source voltage that the present invention proposes, comprise the following steps:
(1) establish three phase network voltage and be respectively e
a, e
b, e
c, three phase network electric current is respectively i
a, i
b, i
c, DC voltage is V
dc, three phase network voltage and electric current are carried out to positive-negative sequence separation and obtain electrical network positive sequence voltage e
a p, e
b p, e
c pwith electrical network negative sequence voltage e
a n, e
b n, e
c nand electrical network forward-order current i
a p, i
b p, i
c pwith electrical network negative-sequence current i
a n, i
b n, i
c n;
(2) to three phase network positive sequence voltage and electrical network forward-order current, through abc/ α β coordinate transform, be the line voltage e under two-phase rest frame
α p, e
β pwith forward-order current i
α p, i
β p, by the positive sequence voltage under two-phase rest frame through α β/dq coordinate transform to electrical network positive sequence voltage e under two cordic phase rotators
d p, e
q p;
(3) according to reference voltage vector, decompose and regard 3 level space vector as six two level space vectors, and the two level locus at the three-phase positive sequence voltage obtaining according to step (1) judgement voltage vector place, making three level depression of orders is two level.
(4) calculate the current reference value under active power reference value and two-phase rest frame;
A) calculate V
dcwith reference value V
dc *between difference, and difference is converted into after pi regulator computing to system active-power P, re-use slip discrete Fourier transform (slide Discrete Fourier Transform, be sDFT) extract the second harmonic component of active power, and eliminated, finally obtaining active power reference value is p
0 *;
B) make rectifier systems average reactive power reference value q
0 *be 0, and for suppressing electric current negative sequence component in three phase network, make i
d n=i
q n=0, by following formula, can obtain the reference current positive sequence component under rotating coordinate system, and through the reference current positive sequence component that the coordinate transform of dq/ α β obtains under two-phase rest frame be
=
E in formula
d p+ e
q p≠ 0; e
d p, e
q pfor the electrical network positive sequence voltage under two-phase dq rotating coordinate system; i
d p*, i
q p*for the rectifier forward-order current reference value under two-phase dq rotating coordinate system; i
α p*, i
β p*for rectifier forward-order current reference value under two-phase α β rest frame; θ is the voltage vector that obtained by positive sequence voltage and the angle of α axle.
Above-mentioned forward-order current reference value is rectifier current reference value i under two-phase α β rest frame
α *, i
β *.
(5) calculate current forecasting value, DC capacitor voltage predicted value and each the sampling period switching device of rectifier under two-phase rest frame and change number;
A) according to current t
kthe line voltage and the electric current that constantly detect, calculate t by Model Predictive Control
k+1current value is constantly
In formula, L is AC inlet wire inductance; R is the internal resistance of AC inlet wire inductance; T
sfor the sampling time of system; i
α p(t
k), i
β p(t
k) be t
ktime be engraved in the actual current value under two-phase rest frame; i
α p(t
k+1), i
β p(t
k+1) be t
k+1time be engraved in the current forecasting value under two-phase rest frame; e
α p(t
k), e
β p(t
k) be t
ktime be engraved in the actual electric network magnitude of voltage under two-phase rest frame; v
α(t
k), v
β(t
k) application in a k sampling period on off state the α β component of corresponding AC voltage.
B) current t
kthe DC capacitor voltage and the electric current that constantly detect, calculate t by Model Predictive Control
k+1capacitance voltage value is constantly
In formula, C
1, C
2for two capacitances of DC side; T
sfor the sampling time of system; V
dc1(t
k), V
dc2(t
k) be t
kmoment capacitor C
1, C
2on actual voltage value; V
dc1(t
k+1), V
dc2(t
k+1) be t
k+1moment capacitor C
1, C
2on voltage prediction value; i
dc1(t
k), i
dc2(t
k) be t
kmoment capacitor C
1, C
2on actual current value.
C) by off state corresponding to each basic voltage vectors of rectifier, utilize on off state and k the sampling period on off state comparison in k-1 sampling period, draw the number n that adopts the action of Cyclical power device at k
c.
(6) according to the current value i under the two-phase rest frame obtaining in step (5)
α p(t
k+1) and i
β p(t
k+1), DC bus capacitor C
1, C
2magnitude of voltage V
dc1(t
k+1), V
dc2(t
k+1) and compare device variation number n with the last sampling period
c, can construct target function g and be
In formula, i
α *(t
k+1), i
β *(t
k+1) be t
k+1moment current reference value; λ
dcfor weight factor corresponding to neutral point voltage balance; λ
nfor weight factor corresponding to control switch frequency.
By target function g, each on off state is assessed above, selected and make target function hour corresponding on off state, and this on off state is controlled to three brachium pontis of three level rectifiers, realize the operation of rectifier.
As further execution mode, the method of utilizing reference voltage to decompose in step (3) is divided into 6 two level space vectors by 3 level space vector, according to electrical network positive sequence voltage, determine that it is in the position of 6 two level space vectors, in calculating to the optimizing of rolling of the basic voltage vectors in two level spaces.
The present invention has following technique effect:
1. the present invention proposes three level rectifier model predictive control methods under a kind of unbalanced source voltage, separated by the positive-negative sequence to line voltage, utilize the space vector position at electrical network positive sequence voltage place, three level are controlled to vector and be converted into two level control vectors, simplify Model Predictive Control Algorithm, reduced optimizing number of times.
2. in control method proposed by the invention, utilize slip discrete Fourier transform (sDFT) to extract the second harmonic in active power, and subtract each other with the active power obtaining through pi regulator, two frequency multiplication pulsation in active power have been eliminated, the moving steady-state behaviour that improvement system is controlled, has improved the quality of power supply.
3. the present invention utilizes Model Predictive Control to control the rectifier under unbalanced source voltage condition, algorithm is simple, can realize the accurate tracking of electric current, the effect of switching frequency is controlled and reduced to the balance of midpoint potential, and this algorithm is convenient to Digital Realization, be suitable for the control under unbalanced source voltage.
Accompanying drawing explanation
Fig. 1 is the main circuit topological structure figure of three-level PWM rectifier;
Fig. 2 is that the separated positive-negative sequence of time expander method is divided spirogram;
Fig. 3 (a) is 3 level space vector and corresponding on off state figure thereof;
Fig. 3 (b) is the sector map to 3 level space vector;
Fig. 3 (c) is according to line voltage positive sequence component sector decision flow chart;
Fig. 4 is slip Fourier transform principle figure;
Fig. 5 is unbalanced source voltage three level rectifier simplified model PREDICTIVE CONTROL structured flowcharts;
Fig. 6 is unbalanced source voltage three level rectifier simplified model predictive control algorithm flow charts;
Fig. 7 (a) is the three phase network unbalance voltage of input;
Fig. 7 (b) is midpoint potential control waveform figure when switching frequency is 1kHz under unbalanced power supply;
Fig. 7 (c) is three-phase current oscillogram when switching frequency is 1kHz under unbalanced power supply;
Fig. 7 (d) is voltage on line side and current waveform figure when switching frequency is 1kHz under unbalanced power supply;
Fig. 7 (e) is the total percent harmonic distortion figure of three-phase current when switching frequency is 1kHz under unbalanced power supply.
Embodiment
Below in conjunction with accompanying drawing, the invention will be further described:
Known according to Fig. 1, e in three-level PWM rectifier main circuit topological structure
a, e
b, e
cfor three-phase alternating current potential source, i
a, i
b, i
cfor three-phase alternating current side electric current, v
a, v
b, v
cfor rectifier bridge input side three-phase voltage, V
dcfor DC voltage, L and R are respectively AC inlet wire inductance and its equivalent resistance, C
1, C
2for DC bus capacitor, DC side load R
lnext equivalent, n is electrical network mid point, and o is that two electric capacity mid points are connected with the mid point of clamping diode, and the voltage on two electric capacity is respectively V
dc1, V
dc2, capacitance current is i
dc1, i
dc2.
Known according to Fig. 2, while utilizing time expander method to carry out the separation of positive-negative sequence component, it is according to being positive-negative sequence characteristic and symmetrical component method, and in positive sequence, negative phase-sequence separation process, its delay time is relevant with phase sequence.According to deriving, can arrive
（1）
（2）
In formula: T=T
s, be the sampling time.By obtaining above
（3）
From above formula (3), negative phase-sequence electromotive force phase phasic difference 120 in electrical network
0, amplitude is identical, so three-phase negative/positive electromotive force adds up to zero, can be by its abbreviation
（4）
In system, exist triangle relation, it can be represented by the formula
（5）
From above formula (5), can utilize time of time delay T/6 to replace the delay time of 2T/3, the computing time of simultaneously considering sampling time and digitial controller in control system, its delay time can be accepted the impact of system, and the formula that obtains of in like manner can deriving (6) is closed and is
（6）
Profit can obtain the positive-negative sequence component of voltage under three-phase imbalance electrical network in this way, after coordinate transform, can obtain again positive-negative sequence component under two-phase rest frame and the positive-negative sequence component under two-phase rotating coordinate system, in like manner, can utilize time expander method to obtain the positive-negative sequence current component of net side three-phase current.While utilizing time expander method to obtain positive-negative sequence component, computing time is short, can improve the computational efficiency of system simultaneously.
Known according to Fig. 3,27 basic voltage vectors and corresponding on off state thereof that Fig. 3 (a) is three-level PWM rectifier, wherein "+" represents two switching tube conductings above of rectifier bridge arm, " 0 " represents middle two switching tube conductings, "-" representative two switching tube conductings below, its corresponding relation free list 1 represents
Table 1 on off state corresponding relation
| S x | S x1 | S x2 | S x3 | S x4 |
| + | 1 | 1 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 |
| - | 0 | 0 | 1 | 1 |
Note: x=a in table, b, c;
In Fig. 3 (b), be that 27 space voltage vectors of three-level PWM rectifier are divided into 6 large sectors, each large sector can be regarded two level space vectors as, and each large sector is comprised of 8 basic voltage vectors.
Fig. 3 (c) is according to the large sector position in positive sequence voltage judgement voltage vector place, in algorithm, only to the optimizing of rolling of the voltage vector in large sector, has greatly simplified algorithm, has reduced computing time, has improved operational efficiency, and in figure, S represents large sector position.
Known according to Fig. 4, the present invention adopts slip discrete Fourier transform (sDFT) method to extract the second harmonic component in active power, not only discrete fourier algorithm (DFT) is simplified, and avoided the impact of High-frequency Interference, can eliminate like this two frequency multiplication fluctuations in active power, improve the performance of system.
In Fig. 4, the principle of sDFT is: establish finite length sequence
x(n), data length is N, and its discrete Fourier transform is
In formula: W
n=e
-j2 π/N.
Formula (7) is launched, can be obtained
（8）
x(n) diagrammatic representation as shown in Figure 4, wherein,
x 0represent first group of data, its corresponding Fourier transform is X
0(k);
x 1the data that represent new sampled point, its corresponding Fourier transform is X
1(k).
（9）
（10）
To in formula (9) substitution formula (10), can obtain
（11）
From formula (11), obtain
x 1fourier transform X
1(k), only need
x 0fourier transform X
0(k), then carry out twice real addition computing and a complex multiplication operation, so greatly simplified computational complexity, improved operational efficiency.
According to sDFT principle, power sequence P (n) is replaced to finite length sequence
x(n), in formula (11), make k=2 obtain the second harmonic component of active power.
Known according to three-level PWM rectifier Model Predictive Control structured flowchart under Fig. 5 unbalanced source voltage, its concrete implementation step is as follows:
(1) calculate the current reference value under active power reference value and two-phase rest frame;
The positive-negative sequence Mathematical Modeling of three-level PWM rectifier under two-phase rotating coordinate system dq is
（12）
Under unbalanced power supply condition, the power equation of its net side can be expressed as simultaneously
(13)
In formula
;
;
;
; P, q is respectively the off line side active power of unbalanced power supply and reactive power.Separating this equation can obtain
（14）
In formula, p
0, q
0for meritorious, reactive power mean value; p
c2, p
s2for 2 cosine of active power, sinusoidal harmonic wave peak value; q
c2, q
s2for 2 cosine of reactive power, sinusoidal harmonic wave peak value.The expansion of its power expression can be expressed as
（15）
Therefore can adopt matrix-style that above formula is simplified, can be write as
（16）
In formula: M
efor the matrix relevant with electrical network electromotive force.
If M
einverse matrix exist, can obtain the control of the three-phase current when the uneven power grid control according to above formula given, its with three phase network gain merit and the expression formula of reactive power as follows
（17）
When three phase network is uneven, in system, have the existence of negative-sequence current, in system, only consider meritorious and reactive power mean value p
0, q
0during control, the relation of average power and given value of current appointment can be expressed as
（18）
In rectifier, for making the operation of system unit power factor, make average reactive power reference value q
0 *be 0, and for suppressing electric current negative sequence component in three phase network, make i
d n=i
q n=0, therefore can obtain the reference current value under two cordic phase rotators, and through the reference current value that the coordinate transform of dq/ α β obtains under two-phase rest frame be
=
（19）
E in formula
d p+ e
q p≠ 0; p
0 *, q
0 *be respectively average meritorious, reactive power set-point; e
d p, e
q pfor the electrical network positive sequence voltage under two-phase dq rotating coordinate system; i
d p*, i
q p*for the rectifier forward-order current reference value under two-phase dq rotating coordinate system; i
α p*, i
β p*for rectifier forward-order current reference value under two-phase α β rest frame; θ is the voltage vector that obtained by positive sequence voltage and the angle of α axle.And the forward-order current reference value now obtaining is rectifier current reference value i under two-phase α β rest frame
α *, i
β *.
In rectifier control system, p
0 *value and rectifier DC side average voltage have direct relation, when outer voltage adopts pi regulator, the output of voltage regulator and the pass of active power are
（20）
In formula, K
vP, K
vIbe respectively ratio and the storage gain of voltage regulator.Because there being second harmonic component in DC voltage, in the active power that makes to obtain, contain two harmonics simultaneously, therefore to active-power P, adopt sDFT to extract second harmonic, and it is eliminated from P, finally obtain average active power p
0 *.
(2) calculate current forecasting value, DC capacitor voltage predicted value and each the sampling period switching device of rectifier under two-phase rest frame and change number;
The Mathematical Modeling under α β coordinate system when a) level PWM rectifier adopts forecast model to control is
（21）
Wherein
,
,
.
To above formula Mathematical Modeling, adopt Euler's formula to carry out forward difference computing
（22）
By obtaining the expression formula of predicted current under rest frame in formula (22) substitution formula (21), be
（23）
Therefore when unbalanced source voltage, according to current t
kthe line voltage and the electric current that constantly detect, calculate t by Model Predictive Control
k+1current value constantly can be expressed as
(24)
In formula, L is AC inlet wire inductance; R is the internal resistance of AC inlet wire inductance; T
sfor the sampling time of system; i
α p(t
k), i
β p(t
k) be t
ktime be engraved in the actual current value under two-phase rest frame; i
α p(t
k+1), i
β p(t
k+1) be t
k+1time be engraved in the current forecasting value under two-phase rest frame; e
α p(t
k), e
β p(t
k) be t
ktime be engraved in the actual electric network magnitude of voltage under two-phase rest frame; v
α(t
k), v
β(t
k) application in a k sampling period on off state the α β component of corresponding AC voltage.
B), in DC side, according to the relation of capacitance voltage, can obtain
（25）
Voltage change ratio dv/dt can be utilized to forward direction Euler's formula, adopted approximate calculation to be
（26）
By in above formula (26) substitution formula (25), can obtain current t
kthe DC capacitor voltage and the electric current that constantly detect, calculate t by Model Predictive Control
k+1capacitance voltage value is constantly
（27）
In formula, C
1, C
2for two capacitances of DC side; T
sfor the sampling time of system; V
dc1(t
k), V
dc2(t
k) be t
kmoment capacitor C
1, C
2on actual voltage value; V
dc1(t
k+1), V
dc2(t
k+1) be t
k+1moment capacitor C
1, C
2on voltage prediction value; i
dc1(t
k), i
dc2(t
k) be t
kmoment capacitor C
1, C
2on actual current value.
C) according to the on off state corresponding to each basic voltage vectors of rectifier shown in Fig. 3 (a), utilize on off state and k the sampling period on off state comparison in k-1 sampling period, draw the number n that adopts the action of Cyclical power device at k
c.
(3) according to the current value i under the two-phase rest frame obtaining in step (2)
α p(t
k+1) and i
β p(t
k+1), DC bus capacitor C
1, C
2magnitude of voltage V
dc1(t
k+1), V
dc2(t
k+1) and compare device action number n with the last sampling period
c, can construct target function g and be
（28）
In formula, i
α *(t
k+1), i
β *(t
k+1) be t
k+1moment current reference value; λ
dcfor weight factor corresponding to neutral point voltage balance; λ
nfor weight factor corresponding to control switch frequency.
By target function g, each on off state is assessed above, by adjusting weight parameter λ
dcand λ
ncontrol the balance of midpoint potential and the height of switching frequency, comprehensive Current Control, midpoint potential are controlled and switching frequency is controlled to select and made hour corresponding on off state of target function, and this on off state is controlled to three brachium pontis of three level rectifiers, realize the operation of rectifier.
During according to Fig. 6 unbalanced source voltage, three-level PWM rectifier low switching frequency Model Predictive Control flow chart is known, first system network side three-phase voltage, three-phase current, DC voltage electric current are sampled, and net side three-phase voltage and electric current are carried out to positive-negative sequence separation; Secondly according to voltage on line side positive sequence component, the sector of 3 level space vector is judged, 3 level space vector is converted into two level space vectors, make vector circulation number reduce to 8 from 27; Then according to the electric current and voltage value detecting, calculate current on line side predicted value and DC voltage predicted value, according to target function, Current Control, mid-point voltage, switching frequency are carried out to rolling optimization again, finally select suitable optimization voltage vector, and export corresponding on off state.
Three level rectifier simplified model PREDICTIVE CONTROL oscillograms under unbalanced source voltage while being 1kHz according to Fig. 7 switching frequency.Fig. 7 (a) is the three-phase imbalance voltage of input; From Fig. 7 (b) DC side midpoint potential waveform, under this control mode, DC side mid point keeps balance, and fluctuation is less; From Fig. 7 (c) current on line side waveform, when this control mode can realize unbalanced power supply, three-phase balance is controlled, and accurately follow current is given; From Fig. 7 (d), rectifier voltage on line side electric current same-phase, can move by unity power factor, and the aberration rate analysis of electric current is known in Fig. 7 (e), and current distortion is less, can realize the grid-connected demand of current on line side.
Claims (2)
1. unbalanced source voltage three level rectifier simplified model forecast Control Algorithm, is characterized in that comprising the following steps:
(1) establish three phase network voltage and be respectively e
a, e
b, e
c, three phase network electric current is respectively i
a, i
b, i
c, DC voltage is V
dc, three phase network voltage and electric current are carried out to positive-negative sequence separation and obtain electrical network positive sequence voltage e
a p, e
b p, e
c pwith electrical network negative sequence voltage e
a n, e
b n, e
c nand electrical network forward-order current i
a p, i
b p, i
c pwith electrical network negative-sequence current i
a n, i
b n, i
c n;
(2) to three phase network positive sequence voltage and electrical network forward-order current, through abc/ α β coordinate transform, be the line voltage e under two-phase rest frame
α p, e
β pwith forward-order current i
α p, i
β p, by the positive sequence voltage under two-phase rest frame through α β/dq coordinate transform to electrical network positive sequence voltage e under two cordic phase rotators
d p, e
q p;
(3) according to reference voltage vector, decompose and regard 3 level space vector as six two level space vectors, and the two level locus at the three-phase positive sequence voltage obtaining according to step (1) judgement voltage vector place, making three level depression of orders is two level;
(4) calculate the current reference value under active power reference value and two-phase rest frame;
A) calculate V
dcwith reference value V
dc *between difference, and difference is converted into after pi regulator computing to system active-power P, re-use slip discrete Fourier transform (slide Discrete Fourier Transform, be sDFT) extract the second harmonic component of active power, and eliminated, finally obtaining active power reference value is p
0 *;
B) make rectifier systems average reactive power reference value q
0 *be 0, and for suppressing electric current negative sequence component in three phase network, make i
d n=i
q n=0, by following formula, can obtain the reference current positive sequence component under rotating coordinate system, and through the reference current positive sequence component that the coordinate transform of dq/ α β obtains under two-phase rest frame be
=
E in formula
d p+ e
q p≠ 0; e
d p, e
q pfor the electrical network positive sequence voltage under two-phase dq rotating coordinate system; i
d p*, i
q p*for the rectifier forward-order current reference value under two-phase dq rotating coordinate system; i
α p*, i
β p*for rectifier forward-order current reference value under two-phase α β rest frame; θ is the voltage vector that obtained by positive sequence voltage vector and the angle of α axle;
Above-mentioned forward-order current reference value is rectifier current reference value i under two-phase α β rest frame
α *, i
β *;
(5) calculate current forecasting value, DC capacitor voltage predicted value and each the sampling period switching device of rectifier under two-phase rest frame and change number;
A) according to current t
kthe line voltage and the electric current that constantly detect, calculate t by Model Predictive Control
k+1current value is constantly
In formula, L is AC inlet wire inductance; R is the internal resistance of AC inlet wire inductance; T
sfor the sampling time of system; i
α p(t
k), i
β p(t
k) be t
ktime be engraved in the actual current value under two-phase rest frame; i
α p(t
k+1), i
β p(t
k+1) be t
k+1time be engraved in the current forecasting value under two-phase rest frame; e
α p(t
k), e
β p(t
k) be t
ktime be engraved in the actual electric network magnitude of voltage under two-phase rest frame; v
α(t
k), v
β(t
k) application in a k sampling period on off state the α β component of corresponding AC voltage;
B) current t
kthe DC capacitor voltage and the electric current that constantly detect, calculate t by Model Predictive Control
k+1capacitance voltage value is constantly
In formula, C
1, C
2for two capacitances of DC side; T
sfor the sampling time of system; V
dc1(t
k), V
dc2(t
k) be t
kmoment capacitor C
1, C
2on actual voltage value; V
dc1(t
k+1), V
dc2(t
k+1) be t
k+1moment capacitor C
1, C
2on voltage prediction value; i
dc1(t
k), i
dc2(t
k) be t
kmoment capacitor C
1, C
2on actual current value;
C) by off state corresponding to each basic voltage vectors of rectifier, utilize on off state and k the sampling period on off state comparison in k-1 sampling period, draw the number n that adopts the action of Cyclical power device at k
c;
(6) according to the current value i under the two-phase rest frame obtaining in step (5)
α p(t
k+1) and i
β p(t
k+1), DC bus capacitor C
1, C
2magnitude of voltage V
dc1(t
k+1), V
dc2(t
k+1) and compare device variation number n with the last sampling period
c, can construct target function g and be
In formula, i
α *(t
k+1), i
β *(t
k+1) be t
k+1moment current reference value; λ
dcfor weight factor corresponding to neutral point voltage balance; λ
nfor weight factor corresponding to control switch frequency;
By target function g, each on off state is calculated above, select and make target function hour corresponding on off state, and this on off state is controlled to three brachium pontis of three level rectifiers, realize the operation of rectifier.
2. three level rectifier simplified model forecast Control Algorithm during unbalanced source voltage according to claim 1, it is characterized in that the method for utilizing reference voltage to decompose in step (3) is divided into 6 two level space vectors by 3 level space vector, according to electrical network positive sequence voltage, determine that it is in the position of 6 two level space vectors, in calculating to the optimizing of rolling of the basic voltage vectors in two level spaces.
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